Application of spray metal linings for aluminum engine cylinders of or for reciprocating engines



Patented Mar. 11, 1952 APPLICATION OF SPRAY METAL LININGS FOR ALUMINUM ENGINE CYLINDERS OF "OR FOR RECIPROCATING ENGINES .Arthur P. Shepard, Flushing,iN.l.Y., assignor to MetallizingiEngineering Co. 1110.; Long Island City, N. Y., a'corporation of NewJersey NoDrawing. .Application December 19,1947, .Serial No. 792,836

7 Claims. ,1

This invention relatesto new and useful improvements in spray. metal linings for aluminum engine cylinders ofor for reciprocating engines.

In the past, there has been no satisfactory means for lining aluminum engine cylinders with sprayed metal. In the construction ofthe aluminum cylinders it has been the practice, in the past, to either construct the cylinders without liners or to construct them with solid sleeveliners, such as cast iron sleeves. These latter are commonly cast in place in the aluminum cylinder by placing them in the mold prior to, thecasting of the aluminum.

Although cast iron liners have, proved relatively satisfactory, the use of them has the disadvantage of high cost of construction, excessive weight, and the limitations of metals which can be used for the liners. Hardened steel liners can notbe used as sleeves for inserts because the heat of casting would soften previously hardened liners and any attempt to harden the liners after casting would be detrimental to the aluminum. Where aluminum is used for engine cylinders without lining, they have been found relatively unsatisfactory becausealuminum is not sufiiciently Wear-resistant to withstand the wearing action of the piston orthepiston rings.

Sprayed metal offers advantageous bearing characteristics due to its porosity and inherent oil retention properties. Furthermore hard sprayed metals can be applied, such as hardened steels, at temperatures which do not. affect the physical properties of the aluminum.

'It has therefore been proposed in the past to line aluminum engine cylinders with sprayed metal so as to overcome the above mentioned disadvantages. These, however, have not proved practical. The primary reason for this resides in the inherent limitations of known means for bonding such sprayed metal coatings to thewalls of the aluminum cylinders.

In metal spraying the metalto be applied is projected against the surface to be covered in the form of a spray, the particles of which are in a molten or heat plastic condition. Asa rule, metal spraying is carried outwith "the use "of metal spray guns, i. e.,devices in which the metal is fed to a heating zone from which zonemetal particles, at least someof'whichare molten or in a heat plastic condition, are propelled against the surface to be sprayed. 'The propulsionmay be --effected either by centrifugal means'or by means of-a'blast of air or other gas. One of the most widely used forms of spraying device is a metal spray gunutilizing the metal to'be'spraye'd 1n= theform of a rod or wire which is fed byua '2 suitable feed mechanism into a heating ,1 zone which is produced by the .combustion of a .combustible and. a combustion-supporting gas. Suchrod or wire may be a relatively solid rod or Wire of such metal, or alternatively it maybe composed of particles of. such metal bonded together by. a suitable binder such as a plastic material. In the latter case the binder is usually of the kind-which willvolatilize asthe result of ;the applied heat of .the spray gun.

, In its application to aluminum engine cylinders it is essential that the applied spray metaladheres to the surface of the cylinderwall with a high degree of bond, for otherwise the applied spray metal may come off. For the purpose of securing therequisite degree of bonding, the. surface to which the spray metal is to beapplied must be,-.as a, rule, suitably pre-conditioned. In the past, such pre-conditioning treatment. has been generally of two kinds, roughening and heating. vRoughening has been carried out by mechanical roughening and also rougheningby the deposition of metalby an electricalfusing.ora welding procedure.

Mechanical rougheningof the aluminumcylinder surface to adapt the same to receive and retain applied spray metalmust be of a type involving the formation of multiple number of closely spaced cavities with peened and splayed edges and interspaces forming a ,multitudeyof keyways. In the.past,,the.most common method of procuring. such type surfaces has been by sand or grit blasting. Sand or grit blasting alone, however, does not, produce a sufficiently strong bond to aluminum to. retain the applied, spraymetal under the conditions of serviceto which analuminum: engine cylinder is subjected.

An alternative .form of mechanical surface roughening for spray metal bonding purposes is that of machine roughening a surface uto be sprayed in a particular mannerdesigned to procure the above mentioned surface characteristics essentialfor spray. metal bonding. ,Such surface roughening methods, however, have the same 'inherent limitation as the ones involving sander grit blasting.

It has been found possible tosecureea moderately strong bond between sprayed metal and aluminum by cutting relatively deep grooves. into the aluminumsurface and thereafter roughening the grooved surface, such as :by sand orgrit blasting. This method has the basic limitation, however, of-being too expensive for, use on mostaluminum' engine cylinders. When this procedure.

is used, the cost of the finished product includes the extra cost of grooving the entire "inside: surface of the cylinder, such as by threading, by the amount of additional sprayed metal which must be sprayed to fill the grooves and particularly by the cost of machining or grinding the sprayed cylinder to remove the eXcess metal which must be sprayed on the ridges between the grooves. Another limitation of this procedure is due to the weakening effect and consequent reduction in fatigue strength of the aluminum cylinder.

Electrical methods of fusing or welding elec trode metal to a base metal to produce a roughened surface consisting of the applied electrode metal have been used as a means for pre-conditioning metal surfaces for receiving and bond ing applied spray metal. This method, however, has the disadvantage of producing only a very weak bond between aluminum and applied spray metal and this bond has proved inadequate for meeting the service conditions required of aluminum engine cylinders.

The heating method of surface conditioning a metallic base to bond thereto applied spray metal involves the heating of the surface to a relatively high temperature and thereafter spraying the hot surface with metal. This method is not widely used and requires, as a general rule, considerable skill and elaborate equipment and is relatively expensive. Furthermore, in the case of aluminum engine cylinders, the temperature to which the surface or base must be heated usually is so high that it tends to seriously weaken the aluminum. A further limitation in the method of heating to produce bonding resides in the fact that aluminum oxidizes to an objectionable degree when heated in air.

There is one basic limitation inherent in practically all of the hitherto used conditioning methods for rendering metal surfaces capable of satisfactory bonding applied spray metal. This limitation resides in the fact that all hitherto used conditioning methods materially adversely effect the surface condition of the base to which they are applied and all such methods require a distinct and costly step of pre-conditioning the base surface before the metal spraying operation can be performed.

One object of the invention comprises, inter alia, a method for applying spray metal to the bore of aluminum engine cylinders which is substantially free from the aforementioned limitations inherent in hitherto known practices.

Another object of the invention is to provide a method for applying spray metal to the bore of aluminum engine cylinders with a high degree of bond and without materially affecting more than a thin skin of the surface of said cylinder bore.

A further object of the invention is an aluminum engine cylinder lined with a spray metal substantially adhering thereto with a high degree ofbond and preferably one substantially harder than the'aluminum of the cylinder.

The foregoing and still further objects of the invention may be seen from the following description:

The method in accordance with the invention essentially embraces an improvement in the application of spray metal to the bore surface of an aluminum engine cylinderwith a high degree of bond, which comprises conditioning such surface for spray metal bonding by spraying at least a flash coating of molybdenum thereon and thereafter spraying a metal, and preferably a metal substantially harder than the aluminum of said bore, onto the thusly coated surface.

1y comprises an engine cylinder having an aluminum bore surface, a layer of spray metal, preferably substantially harder than the aluminum of said bore surface, and intermediate said layer of spray metal and said bore surface, in surface-to-surface bond therewith, sprayed molybdenum of at least flash coating thickness.

Wherever the expression aluminum engine cylinder or similar term is used herein, it is intended to denote thereby the cylinder of any engine having an aluminum or aluminum alloy bore surface and in which a reciprocating piston operates, whether or not the engine is used for the production of power or simply the application of power, such as engine cylinders of, for instance, internal combustion engines, steam engines, gas compressors, pumps, refrigeration compressors, positive displacement hydraulic pumps, etc.

The spray metal lined aluminum engine cylin- Within the broad concept of the invention the molybdenum sprayed onto the aluminum bore surface, to be thereafter coated with spray metal,

rapid onceor twice-over application of the molybdenum spraying gun and not necessarily presenting a continuous coating. The more continuous the coating is, however, the better will be the bonding strength with which the sub sequently applied spray metal will adhere to the base surface. For best results I find it of advantage to apply a substantially continuous flash coating of molybdenum onto the bore surface. Within the preferred embodiment of the invention at least .005 inch and preferably .002 inch of substantially continuous molybdenum coating is recommended. The upper limit of the molybdenum coating is only dictated by practical and economical considerations. Once a coating thickness of the desired bonding characteristics is applied, any additional thickness will not further substantially improve the bonding characteristics of the molybdenum layer.

The metal spraying is preferably carried out by use of a metal spray gun, using wire or rod as a source of metal.

The molybdenum that I may use in accordance with my invention may be pure molybdenum or a molybdenum alloy or composition. In the latter case I prefer a relatively high molybdenum content, such as an alloy or composition having or more molybdenum. I may, however, use any alloy of molybdenum having 60% or greater molybdenum content and alloyed with any other metals which are known to alloy with molybde-.

num.

Wherever the term molybdenum is used herein, it is intended to designate thereby substantially pure molybdenum as well as alloys or compositions containing at least 60% molybdenum. When referring to a molybdenum composition I mean thereby a composition containing finely divided metallic molybdenum in combination with other elements or metal and not necessarily alloyed therewith.

The surface of the aluminum cylinder bore tobe metal sprayed may be perfectly smooth and no roughening or other conditioning treatment other than cleaning (if necessary) is required. The surface to be sprayed upon with molybdenum should, however, be a clean surface.

7 Cleaning may be accomplished satisfactorily in numerous ways, such as by abrasion, light sand blast ing,

acid-etching, andythelike procedures. These are particularly to be used when there is any danger of oxides being present on the surface. If the surface -is relatively clean of oxides and is merely to. be freed from dirt particles or greasy matter, it may suffice if the same is cleaned with a suitable solvent or the like. Ordinarily, if the cylinder has been recently bored Without the use of a lubricantor coolant, a surface emerges sufliciently clean to be immediately sprayed upon with molybdenum.

Any metal which is capable of being sprayed may then be sprayed directly on to the molybdenum sprayed surface. The final metal to be sprayed should be selected according to its characteristics to meet the requirement of the particular engine cylinder being done. For example, a. common metal to use for an ordinary internal combustion engine would be a high carbon steel, in cases where the final finishing can be done by grinding. -Where the finishing must be done by boring with a tool, a low carbon steel could be used. In some cases stainless steel or bronze or other metals are recommended to provide the particular wear-resistant and corrosion-resistant requirements of the particular engine being manufactured.

Sometimes it is advantageous to preheat the aluminum cylinder before the application of the metal sprayed molybdenum and sometimes it is desirable to preheat the cylinder just prior to the application of the final coating of sprayed metal. In either case, the preheating may be unnecessary and is carried out at relatively low temperatures (as compared with the temperatures required by heat bonding methods). The primary purpose of such a preheat step is to cause expansion of the cylinder before the application of. the final sprayed coating to reduce the stress onthe bond at the interface between sprayed coating and aluminum cylinder bore. The temperatures commonlyused for this purpose are of the order of magnitude of about 300 F.

Sometimes it is of .advantage to provide grooves and ridges or other forms of an irregular contour on the surface of the baseto be metal sprayed. Such grooves or other irregular contours have several advantageous functions although they are not a necessary requirement of the procedure set forth in this invention. One of the advantageous functions of grooves or other irregular contours of the base, is the increase in surface area which such contours provide, which results in an increase in bond to the sprayed metal due to such increased area of bonding. Another advantageous function of such contours is the beneficial effect on the structure of the sprayed metal layer. Such beneficial effect is due to the folding of the stratification layers of such sprayed metal structure. Sprayed metal structures resulting from spraying onto a surface with an irregular contour are generally stronger due to the folding of stratifications or laminations than the structures resulting from the spraying of the same metal onto a substantially even surface.

In accordance with the invention, it is entirely practical not only to select a molybdenum or molybdenum alloy for the first coating applied to the surface of the aluminum engine cylinder, but also to use the same or another molybdenum or molybdenum alloy for the subseqently applied spray metal coating. In this case, the entire coating would be of molybdenum. The use of molybdenum for the subsequently applied spray metal layer is particularly advantageous foruthin coatings which must stand considerable :wear.

When within the preferred application of the molybdenum .a metallizing gunof the-wires type is used for the carrying out of my ;inven'tion,.I prefer to use arod or wire of essentially. pure molybdenum produced by sintering wpowdered molybdenum. Such a sintered rodor Wire may be sprayed directly in such. a metallizing gunbut I prefer to mechanically work the sintered material by swaging and/or;.drawing: to; produce.the final rod or wire.

Although the application 1 of one subsequent metal to the first coatingof' molybdenum alloy on the bore surfaceto be metal sprayed hasbeen previously discussed, it is obvious that:.anynumber of different metals maybesubsequently-applied to form as many layers of different kinds. of metal as desired.

The following example is furnished bywayrof illustration but not of limitation:

Example An automotive internal combustionengine aluminum cylinder block is first bored for the'cylinder holes using a conventional machine tool and method. The last boring operation iswdone dry, without oil or cooling fluids, so .as to produce a clean metal surface. Reasonably fast machine feeds may be used since it is notnecessaryto produce-a particularly smooth finish. 'A. reasonable tolerance for the size of this bore. is allowed. such as a tolerance of .005 inch. The size of the bore is made sufficiently over size to provide sufiicient space for the sprayed metal coatingsof the desired thickness. A practical thickness to use in this case is a total thickness of sprayed metal layers of .032 inch measured on a side so that the boreof the cylinder is approximately .064; inch larger than the desired finished size.

The cylinder block is then preheated in an oven to a temperatureof 300 F.

Immediately after heating and while the cylinder block is still hot, a. flash coating, in,this case about .002 inch thick, of molybdenum is .applied to the surface of each cylinder bore by metal spraying. This coating isapplied by a conventional metallizing gunof the wire feed type, utilizing .091 inch diameter sintered and drawn molybdenum wire. An angular gun nozzle-extension is used and held with its nozzle end .at a' distance of about 2 inches from. the. bore; surface. The total length of the extension is about 1.- foot, and it is so constructed-thatthe heatinguand atomizing portion is at theend of the extension. Such an extension is fittedwith an angular nozzle Which sprays at an angle of approximately 40. The extension is advanced co-axially into the cylinder, with the nozzle approximately 21/; inches from the wall of the cylinder. Thus the spray stream is approximately i inches in length and strikes the surface at an angle of about 40. The cylinder is rotated about its center duringthe application of the molybdenum coating and the extension moved co-axially so that the impinging spray traverses the length of the bore surface of the cylinder. The desired thickness may be applied in one or more passes.

After the application of the molybdenum coating and while the cylinder block is still hot, a spray metal coating of a hard metal, in this case .80 per centum carbon steel is applied to the molybdenum sprayed cylinder bores. This coating is applied using the same metallizing gun, 8. A diameter wire of the steel being utilized in the gun and employing a standard spraying procedure by moving the spraying gun nozzle back and forth over the bore surface sufficiently rapidly to produce layers of approximately 003-1306 inch thick with each pass of the gun. The gun is held with its extended nozzle approximately 2' inches distant from the surface of the cylinder. This steel coating is applied to a thickness of approximately .037 inch to .040 inch on a side. This provides a finish allowance of approximately from .005 inch to .08 inch.

The cylinder bores are then ground to the desired size. They are either ground to the final finish size if a ground finish is considered to be satisfactory or they are ground to a slightly smaller size and honed as a final operation if a hone finish is required, Instead of grinding, a tool boring operation may be substituted if the final sprayed metal coating is that of a steel with a lower carbon content, for instance, .10 per centum carbon.

The metal spray gun of the wire feed type used in the above described example is one having a normal capacity for spraying about pounds of a inch .10% carbon steel wire per hour. Guns of different capacity or other metal spraying devices of different type may be used, in which case the particular operating conditions are to be adapted to those regulating the normal spraying procedure of the particular equipment used, and if necessary with the additional provision of appropriate safeguards or adjustment to avoid excessive oxidizing conditions.

The molybdenum wire specified in the example is a commercial sintered and drawn molybdenum wire conventionally designated as black oxide finish-no ,anneal. It is a substantially pure molybdenum wire. Other wires or rods of molybdenum or molybdenum alloys or compositions may be substituted for the specific molybdenum used in the aforedescribed example with good results. Such are, for instance, molybdenum wire or rods commercially designated as hydrogen cleaned and annealed and chemical plus hydrogen cleaned and annealed and also such molybdenum alloys or compositions as 60-40 molybdenum-tungsten, 90-10 molybdenum-tungsten, 70-molybdenum 30-iron, and the like.

During spraying operations it is necessary, as

'for instance set forth in the example, to avoid 9 conditions of oxidation during spraying. The reason is that excessive oxidation of the subdivided molybdenum particles will impair the adhesion characteristics of the ultimately applied spray metal coating to the base. Excessive gas or by utilizing a substantially inert gas as the blast conveying gas for the propulsion of the spray metal or by both the expedients.

Wherever reference herein is made to carbon steel or the like expression, the same is used in its broad connotation, being intended to designate all alloys of carbon and steel including those which also include other alloying elements such as for instance nickel, chromium, vanadium, molybdenum, etc.

The foregoing specific description is for the purposes of illustration and not of limitation and it is therefore my intention that the invention be limited only by the appended claims or their equivalent wherein I have endeavored to claim broadly all inherent novelty.

I claim:

1. A spray metal lined aluminum engine cylinder which comprises an engine cylinder having an aluminum bore surface, a layer of spray metal, and intermediate said layer of spray metal and said bore surface, in surface-to-surface bond therewith, sprayed molybdenum of at least flash coatin thickness.

2. A spray metal lined aluminum engine cylinder in accordance with claim 1 in which said sprayed molybdenum forms a layer of at least about .0005 inch thick.

3. A spray metal lined aluminum engine cylinder in accordance with claim 1 in which said sprayed molybdenum forms a layer of at least about .002 inch thick.

4. A spray metal lined aluminum engine cylinder in accordance with claim 2 in which said molybdenum is substantially pure molybdenum and in which said spray metal layer is composed of a metal substantially harder than the aluminum of said bore surface.

5. A spray metal lined aluminum engine cylinder in accordance with claim 4 in which said spray metal layer is composed of carbon steel.

6. A spray metal lined aluminum engine cylinder in accordance with claim 4 in which said spray metal layer is composed of bronze.

7. A spray metal lined aluminum engine cylinder in accordance with claim 4 in which said spray metal layer is composed of stainless steel.

ARTHUR P. SHEPARD.

REFERENQES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,923,790 Moore Aug. 22, 1933 2,166,634 Lesage July 18, 1939 FOREIGN PATENTS Number Country Date 376,117 Great Britain July 7, 1932 392,145 Great Britain 1933 510,404 Great Britain Aug. 1, 1939 

1. A SPRAY METAL LINED ALUMINUM ENGINE CYLINDER WHICH COMPRISES AN ENGINE CYLINDER HAVING AN ALUMINUM BORE SURFACE, A LAYER OF SPRAY METAL, AND INTERMEDIATE SAID LAYER OF SPRAY METAL AND SAID BORE SURFACE, IN SURFACE-TO-FURFACE BOND THEREWITH, SPRAYED MOLYBDENUM OF AT LEAST FLASH COATING THICKNESS. 